Lighting device

ABSTRACT

An LED lighting device is provided which is capable of being connected to a network and being controlled by a host computer also connected to the network. The lighting device has several lifespan expanding features such as including several extra LEDs such that as the LEDs of the lighting device degrade over time more LEDs can be turned on thus allowing a constant luminosity to be maintained.

BACKGROUND OF THE INVENTION

The current invention is an light emitting diode (herein referred to asLED) lighting device having multiple features designed to allow thelighting device to maintain luminosity as measured in candelas, over itslifespan. The invention is also designed so that multiple lightingdevices can be connected in a network controlled by a host computer,such that the general luminosity over an area (e.g. a tunnel) can becontrolled.

Traditionally, roads and tunnel lighting devices have used uses HID(High-Intensity Discharge) lamps, powered with high-voltage (e.g. 300VAC to 400 VAC).

Existing roadway standards divide the length of the tunnel into a numberof regions. Each region requires a lighting intensity (sometimes hereinreferred to as luminosity) that increases as it is nearer theentrance/exit points (because of the presence of higher illuminationfrom the sun), and decreases towards the middle of the tunnel. As anexample, a typical system can use one 130 W lamp per 1.75 m per roadlane in order to satisfy the daytime specifications required in theInterior Zone of a tunnel.

A problem with current tunnel lighting lamps is with lifespan. In atypical tunnel lamp which uses one or maybe two illumination sources,the lighting device can easily become unuseable should the illuminationsource break down. In these cases the illumination sources need to bereplaced manually before the lighting device can again providesufficient light. It also is necessary to close lanes in the tunnelwhile the maintenance is in progress. Thus maintenance of lightingdevices can become costly and time consuming.

Therefore, a new lighting device which allows for a longer lifespanwithout maintenance is desired. The present invention attempts toprovide such a lighting device using LEDs as illumination sources. Whilean individual LEDs is on its own not sufficient to provide lighting fora tunnel, LEDs only cost a fraction of what a typical HID lamp wouldcost. An LED further uses much less power than that of a typical HIDlamp. Therefore, a plurality of LEDs can be provided for a lightingdevice and the cost and power usage would still be below that of atypical HID lamp. For instance a example LED lighting device couldprovide lighting for the interior of a tunnel, while using 780 LEDs andbeing powered by a 24 VDC power supply.

LED lighting devices are known in the art, though most of these lightingdevices, are use for making billboards and traffic signals. Examplesthese kinds of lighting devices can be found in U.S. Pat. No. 6,175,342Nicholson et al., U.S. Pat. No. 6,150,771 Perry, U.S. Pat. No. 6,150,996Nicholson et al., U.S. Pat. No. 5,514,698 Nicholson et al., U.S. Pat.No. 4,357,671 Miller, U.S. Pat. No. 4,271,408 Teshima et al., and U.S.Pat. No. 4,298,869 Okuno.

Using a plurality of LEDs as a replacement for an standard illuminationsource is less common, but are for instance described in U.S. Pat. No.6,255,786 Yen, and U.S. Pat. No. 6,211,626 Lys et al. These lightingdevices show that LEDs can be used to replace more standard illuminationsources. They do, however, not have features which allow for a constantluminosity to be maintained over an extended lifespan.

Certain patents, such as U.S. Pat. No. 6,236,331 B1 Dussurealt, U.S.Pat. No. 6,153,985 Grossman, and U.S. Pat. No. 5,783,909 Hochstein,propose to compensate for long term LED degradation through a variablecurrent. In these lighting devices, which deal mostly with trafficlights, the luminosity output of traffic lights using LEDs is stabilizedby varying the current flow. The lighting devices measure the luminosityoutput of the LEDs and either increase or decrease the current beingsupplied to the LEDs as a result. The current control is usuallyperformed either through proportional DC (Direct Current) control, orthrough PWM (Pulse Width Modulation) of the LED supply. In the contextof roadway or tunnel lighting, the use of PWM to control the LEDintensity may be problematic. This is because it can lead to visiblestroboscopic beat effects in the light superposition of multiplelighting devices each having slightly different, non-synchronized PWMfrequencies.

It would therefore be advantageous to have a different way ofstabilizing the lighting device's luminosity.

SUMMARY OF THE INVENTION

Therefore the present invention provides a lighting device comprising

-   -   a plurality of groups of light emitting diodes, each of said        groups of light emitting diodes containing one or more light        emitting diodes, each of said light emitting diodes being        configured so as to pass between an energized light emitting        state and a non-energized state;    -   luminosity measuring means for providing a standard luminosity        reading at predetermined time intervals (e.g. from a test        diode);    -   controller means for transferring at predetermined time        intervals, in response to said standard luminosity reading, one        or more of said groups of light emitting diodes between a first        energized group wherein said light emitting diodes are in said        energized light emitting state and a second non-energized group        wherein said light emitting diodes are in said non-energized        state.

In one aspect of the present invention said controller means may beconfigured to maintain all of the light emitting diodes in said firstenergized group when a predetermined luminosity reading is provided bysaid luminosity measuring means.

In one embodiment said luminosity measuring means for providing astandard luminosity may comprise one or more test light emitting diodescoupled to light sensors, such that said test diodes can emit lightwhich will then be measured by the light sensors. This measurement willthen form the basis for said standard luminosity.

The invention further provides a lighting device comprising

-   -   a plurality of groups of light emitting diodes, each of said        groups of light emitting diodes containing one or more light        emitting diodes, each of said light emitting diodes being        configured so as to pass between an energized light emitting        state and a non-energized state;    -   usage time measuring means for providing a usage time        measurement for each of said groups of light emitting diodes at        predetermined intervals (e.g by storing usage times in a memory)    -   controller means for transferring, at predetermined time        intervals, in response to said usage time measurements, one or        more of said groups of light emitting diodes between a first        energized group wherein said light emitting diodes are in said        energized light emitting state and a second non-energized group        wherein said light emitting diodes are in said non-energized        state.

In one embodiment of the present invention said controller means may beset to transfer said groups of light emitting diodes between said firstenergized group and said second non-energized group in response to boththe standard luminosity reading and the usage time measurement.

It should be clear that the controller means can be configured totransfer said groups of light emitting diodes between said firstenergized groups and said second non-energized group in response to anysuitable criteria.

In one aspect of the invention the LEDs may always be used at fullcurrent, and the lighting device's luminosity may be controlled byadjusting the number of LEDs turned On.

This method of using a single current may result in a lower LEDdegradation rate than other methods, because it is known that an LEDused continuously at a fractional current degrades faster than an LEDused for a fractional time at full current, both fractions being equal.

As an example: data provided by Toshiba, a major LED manufacturer, forits TLYH Amber LED series (such as could be used with the lightingdevice) indicates that at 25 deg. C. the LED luminosity will degrade by50% in 170,000 hours when used at lOmA, and in 140,000 hours when usedat 20 mA. If the the LED were used at 20 mA only half the time (therebygetting the same average light as using it continuously at 10 mA), itwould take 280,000 hours to reach the 50% degradation point, lastingsubstantially longer than the 170,000 hours of the continuous 10 mAoption. It can therefore be seen that reducing usage time even whilecompensating with increased current will provide a slower degradationrate.

The invention also provides a lighting arrangement comprising:

-   -   two or more circuit board means, each circuit board means having        a projection axis and a plurality of light emitting diodes, such        that any light emitted by the light emitting diodes on each of        said circuit board means is projected substantially parallel to        said projection axis;    -   said circuit board means being disposed such that each of said        projection axes are disposed at an angle to each other.

In an aspect of the present invention said angle may for example be from5 to 15 degrees.

The invention also provides a network comprising:

-   -   a host computer; and    -   a plurality of light emitting diode lighting devices;        said host computer comprising:    -   means for transmitting a request for a status report from each        of said light emitting diode lighting devices,    -   means for receiving a status report from each of said light        emitting diode lighting devices;    -   and    -   means for transmitting a signal to each of said light emitting        diode lighting devices such that the host computer can direct        how much light each of said lighting devices emits; and        each of said plurality of light emitting diode lighting devices        comprising:    -   means for receiving a request for a status report from said host        computer, creating said status report, and transmitting said        status report to said host computer; and    -   means for receiving a signal from said host computer and        altering how much light said light emitting diode device emits        in response to said signal.

In one embodiment said status report may comprise current luminositysetting, current actual luminosity output, current light emitting diodedegradation, current dirt accumulation, current number of light emittingdiode groups in use, current number of open-circuited light emittingdiode groups and current average usage time of light emitting diodegroups.

The present invention further provides a method for manipulating thelight intensity in a tunnel, said tunnel comprising a lighting systemcomprising a plurality of lighting devices, said method comprising meansfor raising and lowering, in unison, the luminosity level of each ofsaid devices; (e.g. the means for raising and lowering may, for example,comprise a computer in a network as described herein or a suitableswitching means or other control means able to accomplish the desireddimming or increase in light intensity).

The invention further provides a network comprising:

-   -   a host computer; and    -   a plurality of light emitting diode lighting devices;        said host computer comprising:    -   means for transmitting a signal to each of said light emitting        diode lighting devices such that the host computer can direct        how much light each of said lighting devices emits; and        each of said plurality of light emitting diode lighting devices        comprising:    -   means for receiving a signal from said host computer and        altering how much light said light emitting diode device emits        in response to said signal.

The invention further provides a dirt detection system for a transparentsurface, comprising:

-   -   an electromagnetic radiation emitting means for emitting light;    -   electromagnetic radiation measurement means for measuring light;        said electromagnetic radiation emitting means and said        electromagnetic radiation measurement means being configured        such that said electromagnetic radiation emitting means emits a        certain amount of electromagnetic radiation through said        transparent surface, and said electromagnetic radiation        measurement means measuring how much of said certain amount of        electromagnetic radiation is reflected by said transparent        surface and comparing said amount to a base measurement taken        when said transparent surface is free of dirt.

The invention also provides a light emitting diode lighting device,comprising:

-   -   a plurality of groups of light emitting diodes, each of said        groups of light emitting diodes containing one or more light        emitting diodes, each of said light emitting diodes being        configured so as to pass between an energized light emitting        state and a non-energized state;    -   memory means for keeping track of the time each of said groups        of light emitting diodes have been in said energized light        emitting state;    -   energizing means for inducing any of said groups of light        emitting diodes to pass between said energized light emitting        state and said non-energized state;    -   a luminosity measuring system comprising one or more test light        emitting diodes that are equivalent to said one or more light        emitting diodes which make up said groups of light emitting        diodes, and measuring means for providing a luminosity reading        of the light that one or more test light emitting diodes provide        when in said energized state;    -   storage means for storing the luminosity reading provided by        said measuring means;    -   calculation means for calculating the number of said groups of        light emitting diodes which are needed to provide a light of a        desired luminosity, herein referred to as X, said calculation        being based on the luminosity reading stored in the storage        means;    -   partitioning means for temporarily assigning said groups of        light emitting diodes to a first energized group or to a second        non-energized group; and    -   timer means for causing, every time a predetermined time has        elapsed, the luminosity measuring system to provide a new        luminosity reading, and the partitioning means to partition said        groups of light emitting diodes;        said partitioning means comprising:    -   means for causing said calculation means to calculate X,    -   means for selecting the X groups of light emitting diodes which        have spent the least amount of time in said energized light        emitting state and assigning them to said first energized group,    -   means for assigning the remaining groups of light emitting        diodes to said second non-energized group, and    -   means for causing said energizing means to induce the groups of        light emitting diodes assigned to said first energized group to        pass to said energized light emitting state, and to induce the        groups of light emitting diodes assigned to said second        non-energized group to pass to said non-energized state; and        the total number of groups of light emitting diodes (X+Y) in the        lighting device being such that Y is non-empty for the majority        of the lifespan of the lighting device.

In one aspect the light emitting diode lighting device may furthercomprise:

-   -   a heat dissipation mean for dissipating heat generated by said        groups of light emitting diodes.

In one aspect the light emitting diode lighting device may furthercomprise:

-   -   a light emitting diode status monitoring system having means for        monitoring whether any of said groups of light emitting diodes        have become incapable of being energized, and means for        communicating which of said plurality of light emitting diodes        can still be energized to the partitioning means.

In one aspect the light emitting diode lighting device may furthercomprise:

-   -   a dirt detection means being configured to detect the amount of        dirt on the outer surface of the lighting device and        communicating this amount to the calculation means so that the        calculation means may compensate for the dirt by increasing the        light provided by the lighting device.

In one aspect the light emitting diode lighting device may furthercomprise:

-   -   network connection means for connecting to a network, said        network connection means being configured to communicate with a        host computer and the central control unit such that the host        computer may alter said required amount of light.

In one aspect the light emitting diode lighting device may furthercomprise:

-   -   a light emitting diode status monitoring system having means for        monitoring whether any of said groups of light emitting diodes        have become incapable of being energized, and means for        communicating which of said plurality of light emitting diodes        can still be energized to the partitioning means;    -   a dirt detection means being configured to detect the amount of        dirt on the outer surface of the lighting device and        communicating this amount to the calculation means so that the        calculation means may compensate for the dirt by increasing the        light provided by the lighting device;    -   network connection means for connecting to a network, said        network connection means being configured to communicate with a        host computer and the central control unit such that the host        computer may alter said required amount of light; and    -   a status indicator means connected to said luminosity measuring        system, said dirt detection means, and said network connection        means such that if the measured luminosity falls beneath a        predefined amount, the amount of dirt on the outer surface goes        above a certain amount, or if the network connection means is        unable to communicate with the host computer then the status        indicator means will turn on a signal.

It is to be understood herein, that if a “range” or “group ofsubstances” is mentioned with respect to a particular characteristic(e.g. angles, wavelengths and the like) of the present invention, thepresent invention relates to and explicitly incorporates herein each andevery specific member and combination of sub-ranges or sub-groupstherein whatsoever. Thus, any specified range or group is to beunderstood as a shorthand way of referring to each and every member of arange or group individually as well as each and every possiblesub-ranges or sub-groups encompassed therein; and similarly with respectto any sub-ranges or sub-groups therein. Thus, for example,

-   -   with respect to angles from 5 to 15, would include for example        5.1, 5.2, 6, 5 to 6, 6 to 7, 5 to 7, and soon.    -   with respect to wavelengths 0.1 millimeters to 10 nanometres        would include for example 0.09 millimeters, 10.1 nanometres,        10.2 nanometres, 100 nanometres to 10 nanometres, 0.1        millimetres to 100 nanometres, and so on.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of lighting device of the invention mountedon a ceiling.

FIG. 2 shows the configuration of two LED arrays in the lighting deviceof FIG. 1.

FIG. 2A shows the lighting device using the LED arrays of FIG. 2 mountedon a ceiling in a tunnel

FIG. 3 show a side view of an LED array of FIG. 2, having a heatdissipation means.

FIG. 4 shows a diagram of the different parts of the lighting deviceshown in FIG. 1.

FIG. 5 shows a flow chart of the logic of the microprocessor shown inFIG. 4.

FIG. 6 shows a perspective front view of the lighting device shown inFIG. 1, with dirt detection sensors showing.

FIG. 7 shows a side view of the lighting device shown in FIG. 6, withthe casing removed.

FIG. 8 shows a diagram of one example embodiment of a LED statusmonitoring system for use with the lighting device of the invention.

FIG. 9 shows a diagram of another example embodiment of a LED statusmonitoring system for use with the lighting device of the invention.

FIG. 10 shows a diagram of one possible network structure for multiplelighting devices.

FIG. 11 shows a diagram of another possible network structure for agreat number of lighting devices.

FIG. 12 shows a diagram of a lighting area, e.g. a tunnel divided intoseveral zones.

FIG. 13 shows a flow diagram of the logic of the host computer of thenetwork of lighting devices.

FIG. 14A shows a top view of a tunnel mounted with several lightingdevices of the invention

FIG. 14B is a cross-section of the tunnel shown in FIG. 14A along line14-14, showing the ideal lighting profile of a lighting device.

FIG. 15A shows a side view of the projection angle of an LED having asymmetrical projection cone.

FIG. 15B shows a diagram of the projection pattern of the LED of FIG.15A.

FIG. 16A shows a front and a side view of the projection angle of an LEDhaving a oval projection cone.

FIG. 16B shows a diagram of the projection pattern of the LED of FIG.16A.

FIG. 17B shows a side view of the composite projection angle of two LEDsaccording to one embodiment of the invention.

FIG. 17B shows a diagram of the projection pattern of the LEDs of FIG.17A.

DETAILED DESCRIPTION

FIG. 1 shows a: lighting device 1 of the invention, having a lightingdevice casing 2 with a transparent face 3 in front of a LED array 10. Toensure long-term reliability the casing 2 is environmentally sealed, sothat dust and water cannot penetrate inside.

The casing 2 has a shape such that when the lighting device 1 isinstalled in its normal position (e.g. on the ceiling of a tunnel facingdownwards), its light emission axis 4 is tilted by an angle 5 from thevertical axis 6, towards the incoming traffic. This angle 5 can rangefrom −90 to +90 degrees (e.g. 0 to 80 degrees). Light distributionsimulations show that having the angle 5 in the range of 60 to 70degrees allows for optimization of the illuminance. It should of coursebe noted that any sufficient angle may be used.

In the embodiment of the invention shown in FIG. 2, the lighting device1 has as its main illumination source of an array of individual LEDs 10.The LEDs 10 are assembled on one or more printed circuit board sections20, such that the LEDs 10 are perpendicular to the surface of saidcircuit board sections 20. The number and type of LEDs per section canvary, according to the luminance level required of the lighting device.

As an example, a circuit board section can contain 780 LEDs, arranged ina rectangular array of 26×30 LEDs. The lighting device 1 would containone or more such circuit board sections 20.

As can be seen in FIG. 2, the circuit board sections 20 are angled withrespect to each other. The result is that the light emission axes of thecircuit board sections 20 are slightly out of sync with the ordinarylight emission axis 4, for example from 2.5 to 7.5 degrees, though othersuitable angles can be used. FIG. 2A shows the lighting device mountedon a ceiling in a tunnel. The angling of the circuit boards allows forthe lighting device to conform to specific lighting uniformitystandards. And is described in greater detail below.

Some lighting installation standards require specific illuminance levelsover the lighted areas, with a lighting uniformity that must remainwithin certain bounds. Lighting uniformity is usually specified usingthe minimum illuminance over the lighted area (herein referred to asMin), the maximum illuminance (herein referred to as Max), and theaverage illuminance (herein referred to as Mid). As an example,specifications for tunnel lighting typically require a ratio of Min/Maxabove 30%, together with a ratio of Mined 50%.

It has been determined that for tunnel lighting a way to meet therequirements is to use a series of identical lighting devices 1 in acounter beam orientation 290 at regular spacing (herein referred to asD_(device) 292), as illustrated in FIG. 14A. The experiments have shownthat ideally each lighting device should have a lighting pattern with alateral light projection angle A_(lateral) (herein designated with thereference number 294) wider than the vertical projection angleA_(vertical) (herein designated with the reference number 296), i.e. arectangular-shaped intensity profile 298, as shown in FIG. 14B. FIG. 14Bshows the iso curve of an idealized equal lighting intensity boundary,as seen in a cross-section plane perpendicular to the tunnel main axis.FIG. 14A also shows the direction of traffic by arrow 300.

The lighting device of the invention in this embodiment seeks to meetthe specifications for public lighting installations using the abovedescribed method. It should also be noted that while targeted to thisapproach, other embodiments could be conceived in which differentapproaches are used to satisfy the specifications for public lightinginstallations.

The most simple way to match the rectangular light projection pattern298 with a LED lighting device is to use normal LEDs having symmetricallateral and vertical projection angles A_(lateral) 294 and A_(vertical)296 equal to the wider of the required angles (i.e. A_(lateral)), theLEDs being installed on a printed circuit board oriented such that thelight projection axis is aligned with the lighting device light emissionaxis 4. FIG. 15A illustrates this symmetrical approach. The projectionpattern for the symmetrical method can be seen in FIG. 15B, which showsthe circular projection pattern 302 of the approach, with the idealizedprojection pattern 298. As can be seen some light is wasted in the upperand lower vertical areas 304 of the circular projection pattern.

FIGS. 16A and 16B show another way to obtain a better match to theidealized pattern 298, using special LEDs with an oval intensityprofile. FIG. 16A shows the projection angles of the oval LEDs. ClearlyA_(lateral) 294 is wider than A_(vertical) 296. FIG. 16B shows theprojection pattern for the oval LEDs of FIG. 16A. As can be seen, theoval projection pattern 306 is much closer to the idealized projectionpattern 21.

Oval LEDs are available on the market but the choice of anamorphic ratio(A_(lateral)/A_(vertical)) is too limited and the available intensityprofiles do not lead to optimal results. LED manufacturers can developcustom intensity profiles but the cost would be prohibitive.

Another way to obtain a similar pattern is to use normal LEDs withsmaller projection angles and to add special diffusion optical devices(such as lenses or holographic filters) to stretch the intensity profileinto an oval shape similar to that shown in FIG. 16B. The drawback ofthis method is increased complexity and costs.

As can be seen none of the above patterns are really desirable due toincreased cost and wasted light. The present invention thereforeproposes still another approach that is more simple, flexible andcost-effective. Simulations and experiments show that the requiredprojection pattern can be obtained using normal LEDs with a symmetricalprojection angle close to A_(vertical) and installing them on multipleprinted circuit board sections with a slight angular tilt between eachsection so as to stretch the lateral projection angle A_(lateral).

FIG. 17A shows such an arrangement, with 2 LED 10 having a projectionangle “beta” (herein designated with the reference number 308) beingdisposed on circuit board sections 20. The circuit board sections 20 aretilted such that the LEDs are disposed at an angle “Alpha” (hereindesignated with the reference number 310) to each other. FIG. 17B showsthe resulting “peanut-shaped” intensity profile 312. As can be seen forthe figure a very close match to the idealized rectangular pattern 298can be achieved using the peanut-shaped intensity profile 312.

The angles “Alpha” and “Beta” are to be selected, for example, to matchthe road width, the uniformity photometric ratios to be maintained, thedistance between each lighting device and finally by the tilt angle ofthe lighting device. The number of LEDs required by each lighting deviceis determined by the overall illuminance requirement.

As an example, a simulation for lighting devices made of 780 LEDsdistributed on two printed circuit boards at a tilt angle “alpha” of 10degrees, each having 390 LEDs with a projection angle “beta” of 17degrees. Calculations showed that one lighting device per spacingD_(device)=2 meters was required in order to obtain the requiredilluminance for a typical tunnel. This approach yielded good uniformityvalues Min/Max 50% and Min/Mid=75%. Results have shown that in thisapplication the optimal value for the angle alpha will typically bebetween 5 and 15 degrees. It should be noted that other less optimalangles can be used.

The resulting approach is very flexible because it uses standard LEDscurrently available on the market without any special requirement on theintensity profile. The solution is therefore not limited by one LEDmanufacturer's custom design. New lighting devices can also be updatedeasily by developments in LED industry: if more candelas is availableper LED in standard LEDs, the approach can get the benefit of theimprovement without major redesign of the lighting devices.

Moving on to FIG. 3, which shows a heat dissipation means 30 for usewith the lighting device 1. The heat dissipation means in thisembodiment comprises a heat conductive compound 40, and a heat sink 50.The heat generated by the LEDs is transmitted through the heatconductive compound 40 to the heat sink 50, which dissipates it.

The heat dissipation means 30 is included with the lighting device 1since LED output gradually decreases with usage time. As an example, atypical LED will see its light output decrease by 25% after 100,000hours. The rate of this degradation increases as the junctiontemperature of the LED increases. As an example, a typical LED will seethe same degradation in 140,000 hours at 25_C as in 110,000 hours at60_C. It is therefore important to keep the junction temperature of theLED as low as possible, in order to increase its life expectancy.

Most of the heat generated by a LED 10 is dissipated through its leads11. In the lighting device 1 the junction temperature of the LEDs 10 isminimized by the inclusion of heat dissipation means 30. The currentinvention proposes to minimize the LED junction temperature bymaximizing the transfer of heat through the LED leads. This may beachieved as follows:

First the LED leads 11 are cut so that they stick out of the printedcircuit boards 20 to a certain length. Second the space between the LEDleads is filled with the compound 40 which is conductive to heat but notto electrical current. And example of an appropriate compound would be athermally conductive silicone paste. The compound 40 will cover thewhole surface of the printed circuit board on the opposite side of theLEDs. The thickness of the compound 40 should be slightly greater thanthe length of the LED leads 11 so that no leads 11 extend out of thecompound 40. Finally a metallic heat sink 50 is applied in contact withthe compound 40, to dissipate the heat transferred from the leads 11through the compound 40. This heat sink 50 can alternately be integratedwith the body of the lighting device casing 2.

In an alternate method the LED leads 11 can be cut so that they do notprotrude from the printed circuit boards 20. A thermally conductive softelastomer sheet would then be placed between the printed circuit board20 and the heat sink 50. And example of this kind of sheet is made bythe manufacturer Thermagon.

FIG. 4. shows an electronic diagram of the lighting device 1 shown inFIG. 1. FIG. 4 shows that the LEDs 10 are grouped in a plurality ofgroups of LEDs. 60. An example design could have for instance 78 groupsof 10 LEDs each.

Connected to each groups is a constant current source 70 which can turnthe group either on or off. The constant current sources 70 areconnected to a microprocessor 80. The microprocessor 80 is set tocontrol the lighting device, and is in this embodiment of the inventiona controller means. In the case of the current sources 70 themicroprocessor 80 has an energizing means which controls which of thecurrent sources 70 are turned on and which are turned off, therebycontrolling each of the groups of LEDs 60. The energizing meanscomprises in this embodiment a suitably programmed computer method forthe microprocessor 80. This suitable programming meaning being capableof taking as its input two lists of LED groups, one list containing theLED groups which are to be turned on and one list containing the LEDgroups which are to be turned off. The suitable programming furtherbeing capable of signalling each of said current sources 70 to eitheractivate or de-activate based on said lists.

The group structure of the LEDs is desirable because it allows greatcontrol of the LEDs while not taking up as much circuitry as individualcontrol of each individual LED. Furthermore the group structure is veryflexible in allowing for variable dimming of the luminosity level of thelighting device. The luminosity level will be adjustable by controllingthe number of LED groups turned On or Off.

In the example design containing 78 individual LEDs groups per printedcircuit board, the luminosity will be adjustable with a resolution of100/78=1.28%. As can be seen the groups structure method of dimmingallows for great flexibility in dimming and further allows the LEDgroups to use only a single current level thus simplifies the circuitryof the lighting device.

Additionally, to prevent power transients when the tunnel lighting isturned On or Off, or when its dimming level is changed themicroprocessor in each lighting device will automatically make anyluminosity transition gradual. This is achieved by turning LEDs group Onor Off one by one, with a slight time delay between each group.

While in this embodiment the current source 70 is a constant currentsource, it could also be a variable current source. A variable currentsource has certain advantages in that it could be used to implement along term LED degradation compensation system in which the currentsource could supply more power to compensate for lower output by theLEDs over time.

Also connected to the groups 60 is a LEDs status monitoring system 90which monitors the current flowing through the LEDs groups 60 in orderto identify any defective LED groups.

The lighting device further includes a luminosity, measuring system 100which will measure the luminosity of one or more test LEDs 101, in orderto regulate the luminosity output of the lighting device.

The system in this aspect also includes status indicator means 110 whichhas a light that is visible from the outside of the lighting device. Thestatus indicator 110 will be activated by the microprocessor when thelighting device requires servicing. The status indicator 110 normallyhas two modes, but can be extended to allow for further modes. Thenormal modes are NORMAL in which the light is off and the lightingdevice is functioning normally. The second mode is END OF LIFE in whichthe light is turned on. In this mode the lighting device has detectsthat the LEDs have degraded beyond a predetermined cutoff point. In theembodiment of the lighting device shown in FIG. 4, the status indicatorhas two further modes. These first of these modes is CLEANING NEEDED inwhich the light is set to slowly flash. In this mode the lighting devicehas detected that the transparent face of the casing has become toofilthy and that the lighting device requires cleaning. The final mode isNO CONNECTION in which the light is set to quickly flash. In this modethe lighting device has detected that it has lost its connection to anetwork and a host computer. The status indicator, its modes, and howeach mode is detected will be explained in greater detail below.

The lighting device also includes network connection means 120, forconnecting the lighting device to a network 130. Through the network ahost computer can monitor the status of the lighting device, and set theluminosity output of the lighting device.

The lighting device can also include an address setting switch 135 whichcan be access from the outside of the lighting device, either manuallyof through a remote signal. When the address setting switch 135 isactivated a signal is sent through the microprocessor 80 to the networkconnection means 120. The network connection means then contacts thehost computer through the network and request a network address for thelighting device.

Finally, the lighting device contains a non-volatile memory 140, whichcan be used to store various information which the microprocessor 80needs to perform its function. Such information can include the lightingdevices network address, the luminosity of a standard LED, and thecurrent luminosity setting of the lighting device.

The microprocessor 80 shown in FIG. 4, implements several usefulfunctions for the lighting device. In addition to the energizing meanswhich aids in the variable dimming capacity and control of the LEDgroups, the microprocessor 80 has several means which allows thelighting device to compensate for long-term luminosity degradation.These means are timer means which is a software method which keeps trackof time, calculation means which is a software method capable ofcalculating the number of LED groups which are needed to provide therequired light, and partitioning means which is a software method forselecting which LED groups to turn on. Each of these means will bedescribed in greater detail below.

One main long-term luminosity degradation compensation of the system maybe based providing more groups of LEDs than are require at the start ofthe life cycle of the lighting device. The number of LEDs required togenerate the specified luminosity of the lighting device at the start ofits life-cycle can be determined using the initial LED specifications.It is known that as the LEDs age, their output luminosity will graduallydecrease, or equivalently more LEDs will be required to achieve thespecified luminosity. The lighting device may therefore be designed witha number of extra LED groups which are sufficient to maintain itsspecified luminosity up to the end of its life-cycle. The number ofextra groups of LEDs varies, and the calculation of this number will beexplained in greater detail below.

At certain intervals in the life-cycle of the lighting device, the timermeans of the microprocessor causes the calculation means to calculatethe number of necessary LED groups. This calculation is based on anidealized LED luminosity which it obtains from the luminosity measuringsystem 100, as shown in FIG. 4. As the luminosity of the test LEDs ofthe luminosity measuring system 100 degrade the calculation means willturn on more of the extra LEDs groups to maintain the luminosity of thelighting device. Which of the groups to turn on is selected by thepartitioning means, which follows an algorithm which will be describedin greater detail below.

The number of extra LED groups may be estimated as follows:

Estimation of the Number of Extra LED Groups:

The LED Array of the lighting device is designed with a number of extraLEDs groups sufficient to maintain its specified luminosity up to theend of its life-cycle. The life-cycle of the lighting device ispredetermined and may be for instance between 10 and 15 years. The extraLEDs groups will gradually be used as the lighting device ages.

The number of extra groups is determined as follows, using this set ofdefinitions: L_(tot) = Total  Luminosity  of  the  lighting  deviceN_(on)(t) = Number  of  groups  turned  On  (as  a  function  of  time)  to  maintain  constantL_(tot)L_(led)(t) = Luminosity  (as  a  function  of  usage  time)  for  a  typical  LEDt_(elc) = End-of-  Life-Cycle  time    n_(led) = Number  of  LEDs  per  groupN_(start) = Number  of  LED  groups  needed  at  life-cycle  startup  (t = 0)N_(extra) = Number  of  extra  groups  needed  to  maintain  Total  Luminosity  L_(tot)  at  End-of-Life-Cycle  time  t_(elc)N_(group) = Total  number  of  groups  in  lighting  device

At any given time, the microprocessor monitors L_(lcd)(t) through themonitor LEDs. It then adjusts the number N_(on)(t) of groups turned Onso that the Total Luminosity L_(tot) of the lighting device remainsconstant, according to the following relation:L _(tot) =N _(on)(t)*n _(led) *L _(led)(t)   (1)

From which is obtained:N _(on)(t)=L _(tot) /{n _(led) *L _(led)(t)}  (2)

At start of life-cycle (t=0):N _(start) =N _(on)(0)=L _(tot) /{n _(led) *L _(led)(0)}  (3)where L_(led)(0) is the start-up LED luminosity.

N_(on)(t) will gradually increase as L_(led) decreases with LED age. Thetotal number N_(group) of LED groups in the lighting device must be highenough to satisfy (2) at the End-of-Life-Cycle time, when LED luminositywill be at its minimum:N _(group) =N _(on)(t_(elc))   (4)

After combining (2) and (4):N_(group) =N _(on)(t _(elc))=L _(tot) /{n _(led) *L _(led)(t_(elc))}  (5)

Since by definition:N _(extra) =N _(group) −N _(start)   (6)(3), (5) and (6) can be combined to obtain:N _(extra) =L _(tot) /{n _(led) *L _(led)(t _(elc))}−L _(tot) /{n _(led)*L _(led)(0) }  (7)

The End-of-Life-Cycle luminosity L_(led)(t_(elc))can be obtained fromthe LED manufacturer's specifications sheet. This value is alsodependent on ambient temperature and LED junction current, so thesefactors must be taken into account when evaluating the number N_(extra)of extra LED groups for the lighting device.

Equation (7) is in fact a worst-case approximation of N_(extra), becauseby using L_(led)(t_(elc)) as the End-of-Life-Cycle LED luminosity it isassumed that the LEDs are always On during the full life-cycle of thelighting device. This is in practice not the case because in the earlylife of the lighting device, only N_(start) groups out of the totalN_(group) are On. This means that on average the LEDs degrade lessrapidly than estimated with (5).

The average degradation of each LED may be further improved by anautomatic LED usage equalization mechanism implemented in the lightingdevice. In this mechanism, the microprocessor continuously performs arotation of the LED groups turned On. This rotation is kept slow enough(e.g. once per hour) so as not to be noticeable by casual observers. Inthis way, even if not all groups out of the total available N_(group)are required during the lighting device's early life, all N_(group)groups are still exercised equally on average and therefore degradeequally in the long term. The automatic LED usage equalization mechanismwill be explained in greater detail later.

Taking this mechanism into account, a new reduced value for the numberof extra groups N_(extra) herein referred to as N_(extra)) is obtained.This involves an integration of the LED luminosity L_(led)(t) over theaveraged actual LED On time during the complete lighting devicelife-cycle. Typically N_(extra) can be reduced by a factor of 20% to 50%over the value N_(extra) given by (7), depending on the specificLuminosity curve L_(led)(t) of the LEDs during the lighting devicelife-cycle.

Example of Values Obtained for a Typical Lighting Device:

Below are shown example values obtained for a lighting device usingtypical Amber-colored InGaAlP LEDs.

The following is assumed:

-   -   L_(tot)=1500 cd (candelas) total lighting device luminosity    -   n_(led)=10 LEDs per group    -   t_(elc)=10 years End-of-Life-Cycle time    -   T_(ambient)=25° C. ambient temperature    -   I_(junction)=20 mA (milliAmperes) LED junction current

The LED manufacturer specifies:L_(led)    at  start-up  time  (t = 0)   = 3.5  cd  (candelas)L_(led)    at  End-of-Life-Cycle  (t = 10  years) = 55%  of    L_(led)(0)   = 1.92  cd

According to (3):N _(start) =L _(tot) /{n _(led) *L _(led)(0)}=1500/(10*3.5)=43 LEDgroups needed at start-up.

According to (5):N _(group) =L _(tot) /{n _(led) *L _(led)(10y)}1500/(10*1.92)=78 LEDgroups needed at End-of-Life

Therefore, according to (6):N _(extra) =N _(group) −N _(start)=78−43=35 extra LED groups tocompensate for LED degradation

Taking into account the Automatic LED Usage Equalization mechanism:N _(extra)=25 extra LED groups, or a reduction of about 28% over N_(extra)

For the long term degradation compensation of the lighting device to beeffective it is important that the calculation means has an accurateidea of the current luminosity output of the LED groups. Therefore, inaddition to the LED groups, this system will use one (or more) test LED101 opto-coupled to a light intensity-measuring device 102, as shown inFIG. 4. The light intensity measuring devices 102 can be for instancephotodiodes or any appropriate light sensor. When desired the lightintensity-measuring devices 102 can measure the luminosity output of thetest LEDs 101, and obtain a standard luminosity for the LEDs of thelighting device.

The test LEDs 101 will be identical to the LEDs used in the groups,supplied with the same constant current, kept at the same temperature asthe group LEDs, and turned On and Off in such a way as to maintain orreflect the same or analogous long-term usage rate as the group LEDs, asdescribed below.

As will be described in details later, the lighting device has acontroller means to count and store the cumulative usage time duringwhich each LED group is activated, and further implements an AutomaticLED Usage Equalization mechanism to ensure that on average all LEDgroups are used for the same cumulative time. The same controller meansalso counts and stores the cumulative usage time of the test LEDs, andat regular intervals automatically activates the test LEDs long enoughto ensure that their cumulative usage time is equal to that of the groupLEDs.

For example the controller means could activate test LEDs every time theaverage cumulative usage time of the lighting LEDs exceeds thecumulative usage time of the test LEDs, and turn the test LEDs off everytime the cumulative usage time of the test LEDs is greater than or equalto the cumulative usage time of the lighting LEDs.

The light intensity-measuring device 102 coupled to the test LEDs 101 isread by the controller means. By comparing the test intensity to areference value, the calculation means can estimate the LED luminosityvariations at any given moment and compensate by adjusting the number ofLEDs groups turned ON, thereby regularizing the overall lighting deviceluminosity.

The comparison to the reference values can be seen in FIG. 5, referencenumber 180. The test intensities L1 and L2 are measured in 176 and 178.These values are then compared to reference values Lr1 and Lr2 which areset during the calibration of the lighting device (154, 156, 158). TheLED degradation factor F1 is calculated using the following formulaF1=((L1/Lr1)+(L2/Lr2))/2. As can be seen from the formula the LEDdegradation factor is averaged over the test diodes such that in thecase of abnormal behaviour in one test LED the results will not becompletely skewed.

Number of Test LEDs Provided with a Typical Lighting Device:

It is preferable to have more than one Test LED, in case the Test LEDfails or has abnormal degradation behavior. The probability of theseoccurrences simultaneously to more than one LED is proportionallysmaller.

Since LEDs have a typical MTBF (Mean Time Before Failure) in themillions of hours, the probability of these occurrences for one LED isalready very low during the lighting device life cycle. Therefore using2 test LEDs is considered sufficient to obtain a very reliable system.

The number of test LEDs is not related to the number of lighting LEDs inthe lighting device: the test LEDs' behavior is independent of thenumber of lighting LEDs.

Separate Test LEDs

In order to provide an accurate picture of the lighting device'slighting LEDs state, the test LEDs must operate under identicalconditions: same junction current, same temperature, same usage time.

The most direct way to accomplish this is simply to use some of thelighting LEDs as test LEDs. However this has the following drawbacks:

Each test LED must be optically coupled to a light intensity-measuringdevice, such as a semiconductor photo-sensor. Furthermore, no outsidelight must filter in this coupling, so that the intensity measurementaccurately reflects the Test LED intensity. Such a coupling+photo-sensorassembly can take a substantial amount of physical space in front of theTest LED (typically at least one inch). Using a lighting device'slighting LED as Test LED would require to provide this space between thewhole LEDs PC-Board and the lighting device's transparent displaywindow, therefore substantially increasing the overall lighting device'sdimension.

Because of the automatic LED usage equalization mechanism, the lightingLEDs groups are turned On and Off in an unpredictable way as thelighting device ages and the LED groups' usage goes through a rotation.It can therefore be impractical to wait until a particular lighting LEDused as Test LED is turned On by this mechanism in order to be able tomake an intensity measurement.

Lighting LEDs are organized in groups of typically 10 LEDs. If a singleLED out of a group fails and becomes open-circuited, the whole groupfails. This means that the MTBF of a complete group is substantiallysmaller than the MTBF of each LED. Using a lighting LED as Test LED istherefore less reliable than using an individually connected Test LED.

To overcome these issues separate test LEDs driven with individualcurrent sources can be used. In order to obtain an accurate operation,the following precautions are taken:

Test LEDs are driven with the same junction current as the lightingLEDs.

Thermal modeling inside the lighting device shows that the ambienttemperature is quite equalized throughout the lighting device. Thereforethe test LED ambient temperature is close to or the same as that of thelighting LEDs.

The microprocessor implementing the automatic LED usage equalizationmechanism simultaneously turns the test LEDs On and Off so that theymaintain an averaged usage time equal to that of the lighting LEDs.Because they are independent from the lighting LEDs, the test LEDs canbe turned On whenever intensity measurements are required.

These precautions ensure that the test LEDs will degrade in the same wayas the lighting LEDs.

Automatic LED Usage Equalization

At each stage in the course of the lighting device life, a variablenumber of LEDs groups will be On or Off, according to the dimming levelrequested and the luminosity compensation mechanism. The memory means140 shown in FIG. 4, will keep count of the usage time of each of theLEDs group in the LED Array, and store these individual usage timevalues.

When selecting which LEDs groups to turn On at any given time, thepartitioning means will automatically prioritize the use of LEDs groupshaving the shortest usage time. This prioritization is achieved byprogramming the partitioning means to follow the following algorithm:

-   -   sort the LED groups by usage time;    -   selecting the appropriate number of groups with the least amount        of usage time.

This prioritization will ensure that all LEDs have an equalized usagetime with no LED degrading faster than others, therefore optimizing thelong-term luminosity degradation and stability of the lighting device.

The interconnections of the timer means, calculation means, luminositymeasuring system, and the partitioning means can be seen in greaterdetail in FIG. 5, which shows flow of logic in the microprocessor 80shown in FIG. 4.

After boot initialization 150 the microprocessor waits. Periodically itchecks whether a communication has been received from the network. Thelighting device can receive three kinds of communications, a calibrationcommand 154, mainly used during factory start-up, which causes referencevalues for luminosity degradation calculation to be set; a set intensitycommand 160 which causes the light intensity output of the lightingdevice to be set to a new value 162; and a send status command 164 inwhich the lighting device is requested to send its status to the hostcomputer. The status of the lighting device includes all pertinentinformation, comprising current luminosity setting, current actualluminosity output, current LED degradation factor, current dirtaccumulation factor, current number of LED groups in use, current numberof open-circuited LED groups and current average usage time of LEDgroups. For definitions of these factors and numbers please see below.

If no communication has been received by the lighting device for apredetermined time then the lighting device assumes that its link to thenetwork 130 has been lost and sets the status indicator 110 (see FIG.4), to the NO COMMUNICATION mode.

Finally the microprocessor, periodically recalculates the number ofactive groups in the lighting device and rotates the active groups. Seenin FIG. 5, this happens when the microprocessor checks the timer meansin 174. If a certain interval has elapsed, the luminosity measuringsystem as seen in FIG. 4, is activated and new luminosity readings aretaken, and the percentage of LED degradation factor is calculated (176,178, 180). This new LED degradation factor is checked against a presetvalue (for instance 55%) to see if the lighting device has reached itsend of life. If yes then the status indicator 110 (see FIG. 4), is setto the END OF LIFE mode.

At this point an optional dirt detection means may be called into use.Turning to FIGS. 6 and 7, which show the dirt detection means comprisingof a plurality of light sensors 200, disposed inside the lighting device1. The dirt detection means functions as follows:

The lighting device's light source sends out light outside the lightingdevice through the transparent face 3. When the transparent face 3 isclean, there is hardly any light reflection inside the lighting device.On the other hand, as the dirt level increases, so does the lightreflection level. Therefore, the light sensors 200 will measure thelight level reflected inside the lighting device, determine the dirtlevel, compare both results with preprogrammed data in themicroprocessor, and, if required, trigger an alarm informing thelighting device network operator of the current status.

In an alternate embodiment the sensors 200 can be set to detectelectromagnetic radiation corresponding to a wavelength from 0.1millimeters to 10 nanometers (i.e. Infrared, visible, and ultravioletlight). The sensors would in this embodiment of course be coupled withlight emitting diodes which emit electromagnetic radiation of theappropriate wavelength.

For example, in one embodiment infrared emitters coupled with infraredsensors (e.g. at 940 nm) may be used. The infrared sensor may be chosenwith a bandwidth low enough to reject the visible light coming from thelighting LEDs of the lighting device. This is to ensure that the dirtmeasurements remain independent of the lighting LEDs output, which canvary over time in unpredictable ways due to varying luminosity settingsas set by the network host computer, as well as due to the LED UsageTime Equalization mechanism which constantly varies the activation ofLED groups.

Turning back to FIG. 5, which shows the dirt detection system beingcalled upon and providing a dust masking factor Fd to be measured. Ifthe dust masking factor Fd is under a preset number (in this case 75%)the status indicator 110 (see FIG. 4), is set to CLEANING NEEDED mode.

After the luminosity measuring system and the dirt detection means arefinished the calculation means is activated to calculate the number ofgroups which are required to provide sufficient light based on the setluminosity, and the amount of LED degradation, and the dirt on thetransparent face.

The formula used for this calculation is X=(Nstart*I)/(Fl*Fd). In theformula X is the number of groups required to provide the luminositywhich is desired. Nstart is the total number of LED groups used at thestart of the lighting device's life-cycle. I is the luminosity settingof the lighting device, with 0 being no light and 1 being maximumlighting. Fl is the LED degradation factor, with 1 being no degradationand lower values indicating LED degradation. E.g. a value of 0.5 wouldindicate that the LEDs are only giving off half of their originalluminosity. Finally, Fd is the percentage of light going through thelighting device's transparent face, with 1 being full transmissivity andlower values indicating light lost due to dirt. E.g. a value of 0.5would indicate that only half of the light is going through thetransparent face of the lighting device.

After the calculation means calculated X, the partitioning means isactivated (194, 196). The partitioning means sorts all the LED groups byusage time, and then selects the X groups with the least amount of usagetime. These X-groups with the least amount of usage time are thenassigned to a first energized groups, while the remaining LED groups areassigned to a second non-energized group. The energizing means is thencalled on to energize the members of said first energized group and tode-energize the members of said second non-energized group.

FIGS. 8 and 9 show in more detail the LEDs status monitoring system 90.The system 90 monitor on-demand the LEDs integrity by measuring whetherany LEDs groups are open-circuited. A simple way to achieve thisfunction is shown in FIG. 8, and functions by the following process:

Turn Off all LED groups.

At the common supply point of all LED groups, install in series with thesupply line a test optocoupler 210.

Turn On one LEDs group; if it functions normally, the current it drawswill turn On the test optocoupler 210. If one or more LED in the groupis open-circuited, the group will draw no current and therefore the testoptocoupler will remain Off. The test optocoupler output is monitored bya microprocessor input.

Successively turn. On each of the LEDs groups in the LEDs Array andmonitor them.

Once the test is finished, remove the test optocoupler from the supplyline and resume normal operation.

Another way of accomplishing the LED status monitoring system is bycontinuous monitoring. In this version, shown in FIG. 9, the system isaccomplished by adding current sensing inputs 220 on each LED groups,and multiplexing them to the lighting device's microprocessor. Thismethod allows for monitoring the LED groups' status without interruptingthe lighting device's normal operation, at the cost of substantiallymore circuitry.

Testing Procedure Activation

The LED status monitoring system with the first method requires aninterruption of the lighting device's normal operation. During themeasuring process, all groups are turned Off and each is then turned Onone by one while its current is measured by the lighting device'smicroprocessor; open groups will report zero current. The time requiredto perform the measurement will typically be around 10 ms per LED group;therefore for a typical lighting device with 78 LED groups the completetesting procedure will take around 1s.

Because this testing procedure will be visible from outside (thelighting device will stop functioning normally during a second or so,and display a moving light pattern as each LED group is activated one byone), it cannot be performed too often. It will typically be performedonce per 24 hours.

The testing procedure can be triggered in two ways:

-   -   1. The lighting device's microprocessor can perform the testing        procedure on its own, through a built-in timer with a        programmable period. Each lighting device contain a timer        counter, automatically synchronized to the same time-of-day by        the network host computer so that all lighting devices in the        network have a synchronized time base.    -   2. Upon receiving a specific command from the network host        computer.

In both cases, it is preferable to stagger the testing procedure foreach lighting device in the network, so that normal operation isinterrupted for only one (or a few) lighting device(s) at a time. Inthis way all lighting devices in the network can eventually be monitoredwithout compromising the lighting level provided by the whole system.

The status indicator 110 as seen in FIG. 4, is a light which is visiblefrom the outside of the casing 2. Under control of the microprocessor,the status indicator 110 will provide the following information aboutthe current state of the lighting device: Indicator State StatusDescription Off Normal Normal operation Slow Flashing Cleaning Thetransparent face of the lighting Needed device has accumulated an excessof dirt Fast Flashing No The communication link with Communication theHost PC is lost On End of Life The lighting device can no longer provideits specified luminosity, due to LED failure or degradation.

“Cleaning Needed” Status:

The lighting device's built-in dirt detection sensor has determined thatdirt accumulation on the face plate has decreased luminous intensity bya factor greater than a predetermined threshold value (typically 25%).To make this status clearly visible for a service team on the ground,the Status indicator is flashed at a slow rate.

“No Communication” Status:

The lighting device expects to receive commands at regular interval fromthe network Host PC (typically a few minutes). When this time-outinterval (as measured by the lighting device's built-in timer) isexceeded, the lighting device detects the absence of communication andreverts to a “Default” condition. This Default condition can include thefollowing properties:

-   -   1. Fast Flashing of Status Indicator    -   2. Going to full intensity, to ensure that the worst-case        lighting needs are fulfilled.

“End of Life” Status:

As the lighting device ages and the luminosity of its LEDs decreases,more and more LED groups are turned On to maintain a constant totalluminosity. Eventually all available LED groups are required to achievethe full-intensity state. From that time onwards, the lighting devicefull-intensity luminosity will gradually decrease. To indicate this “Endof Life” status, the Status Indicator is turned On by the lightingdevice's microprocessor.

This event can be accelerated if some LED groups actually fail (becomeopen-circuited), as detected by the LED status monitoring system, sincethe pool of available LED groups is correspondingly reduced.

Note that at this “End of Life” point the lighting device is stilloperational, and may maintain a sizable proportion of its full-intensityluminosity for more years. Also, lower luminosity states (as selected bythe network Host PC, for example during night time) can still becompletely within specifications, as they may require fewer LED groupsthan the total available.

In one embodiment of the invention lane use signals may be included inthe lighting device. In this embodiment each lighting device willincorporate a set of diodes (besides the ones being used for lightingpurposes) which will serve as lane use signals in order to informmotorists on current road conditions. A red X will indicate that thelane is closed. Furthermore, one or many other signals can beincorporated according to prevailing circumstances. A green arrow willindicate that the lane is open, and if motorists have to be instructedto change lane (left or right), a yellow arrow pointing in theappropriate direction can be displayed. These signals can have acontinuous or flashing display and will be controlled by the operator. Acommand is sent by the system operator from the host computer connectedby the network connection means to each lighting device or lightingdevice's controller.

When a lane use signal is being displayed, the operator can send anothercommand from the host computer through the network, to reduce theselected lighting device's brightness to the desired level, in order toenhance contrast for better visual impact of the signal. This commandfunction is most often used in conjunction with the lane closed signal(the red cross). This is because, since the lane is closed then itrequires less lighting. A moderate level such as for instance 50% of thelighting device's nighttime setting (e.g. 1.25 cd/²) will usually besufficient to provide adequate lighting.

A detection and protection mechanism will prevent displaying more thanone signal concurrently on the same lighting device in order to avoidconfusion and potentially dangerous situation or motorists. Thedetection and protection mechanism will work in conjunction with the LEDstatus monitoring system 90, and the microprocessor 80 as seen in FIG.4. The LED status monitoring system will be connected to the signal LEDsand to the microprocessor such that the LED status monitoring systemmonitors the signal LEDs and reports to the microprocessor. Themicroprocessor contains means for receiving the status of the signalLEDs from the LED status monitoring system and checking whetherconflicting signals are being displayed.

An appropriate communication mechanism will return information to thesystem operator concerning the current status of the signals beingdisplayed on the network's lighting devices.

For instance the appropriate information can be appended to the lightingdevice status report which the host computer will periodically requestfrom each lighting device. The host computer can then receive theinformation and interpret it as necessary.

One useful part of the lighting device of the invention is the linkingof a number of lighting devices to a network 130, and their control bythe host computer through this network. This systems-level aspect of theinvention brings a number of further capabilities and features.

Any communication network allowing multidrop connection of a largenumber of lighting devices to the host computer is suitable. As anexample, the following protocols can be used: RS-485, Ethernet, TCP/IP.

FIGS. 10 and 11 show example networks of lighting devices. FIG. 10 showsan example network topology with only a few lighting devices forinstance less than 128 devices. FIG. 11 on the other hand shows a largernetwork with a large number of lighting devices, for instance greaterthan 128 devices. In this network topology the lighting devices aregrouped into individual nodes of less than 128, and node controllers 235are included to relay information between the host computer and thelighting devices.

Each lighting device 1 on the network will be assigned and individual,unique address. The system is designed so that the host computer keeps arecord of the physical location of each lighting device, referenced byits network address.

The address of each lighting device is stored in non-volatile memorywithin its electronic circuit. The lighting device is equipped with anaddress setting switch, accessible from the outside of the case, forinstance physically or through remote controlling means such asinfrared, laser or Radio Frequency signals. At system installation, thisswitch is activated to signal to the Host PC that the lighting device isrequesting a network address, which is then generated and assignedautomatically to the lighting device by the host computer.

The network linking of a number of lighting devices with a host computerhas the following advantages:

-   -   1) Using the Host-to-lighting device communication direction        allows the host computer to control important global aspects of        the lighting system, such as the lighting intensity in specific        zones of the system as a function of the time-of-day and/or        ambient illumination, gradual dimming of lighting intensity in        intensity level transitions, and activation of special functions        such as integrated lane use signals.    -   2) Using the lighting device-to-Host communication direction        allows the transfer of lighting devices status information to        the host computer

These elements are now described in greater details:

One of the functions of the host computer can control the overall orGlobal Intensity level of a lighting area An example of this is shown inFIG. 12, which shows the lighting area (in this case a tunnel) beingdivided into three zones: A threshold zone 242, a transition zone 244,and an interior zone 246.

Because it has individual control over each lighting device, the hostcomputer can vary the intensity level for each specific zone of thelighting area. For example, in a typical tunnel the daytime illuminationin the threshold zone 242 will be set at 200 cd/m², the inner zone 246at 5 cd/m², and the transition zone 244 at intermediate intensities.

The number, size and location of the lighting zones can be easily andarbitrarily modified through the Host software.

Another example of variation controlled by the host computer is theintensity level according to the time of day, and/or the ambientillumination.

According to standard requirements specified by the IlluminationEngineers Society of North America in their document RP22-96illumination in the interior a tunnel should be at least 5 cd/m² in thedaytime, and 2.5 cd/m² in the nighttime. As the lighting requirementsfor nighttime are substantially smaller than those of daytime, thesystem can reduce energy consumption by lowering the intensity duringthe nighttime.

To achieve this task the host computer can be equipped with a ambientillumination sensor at the entrances to the tunnel. The host computerwould then use these sensors to detect ambient illumination. The ambientillumination measurement could then be used to adjust the light of thetunnel. Typical recommendations call for maintaining the threshold areaillumination at least at {fraction (1/10)}th the level of the ambientillumination during daytime.

When changing from one Intensity level to another, the Host can generategradual Intensity transitions in order to maximize energy efficiency.

For example, when changing from Night to Day luminance levels, adiscrete control system would have to select the Day level as soon asmorning ambient light starts to grow. Instead, the host computer canperform a gradual ramping between Night and Day levels, thereby delayingthe increased energy consumption of the day level and enhancing drivers'visual comfort. The ramping can be triggered when the ambientillumination reaches a predetermined level (typically 100 cd/m²) andlast for a user-adjusted length of time (typically 30 minutes).

Another important function of the host computer is monitoring lightingdevice status. At certain intervals the host computer will poll eachlighting device on the network, to obtain its current statusinformation.

This information can be tabulated and logged; alarms can be triggered ifany potential failure or degradation is detected; and maintenancereports can be generated, listing the location and identification ofeach lighting device requiring servicing.

To prevent the loss of tunnel illumination under any circumstance (shortof power failure), each lighting device will automatically revert to itsnormal Intensity level whenever contact with the host computer is lostfor a time interval longer than an adjustable Communication Time-Outperiod. In case of power failure, the system can facilitate thegeneration of emergency lighting backed up by UPS (Uninterruptible PowerSupply). The energy consumption can be reduced to a minimum, either bygreatly dimming the lighting devices, or by dynamically alternating thelighting devices in the On state.

In order to reduce energy consumption, the host computer can detect thepresence of vehicles in the lighting area (through standard VehiclePresence Detectors), and dim the Intensity level when no vehicle ispresent. This dimming can be further refined on a zone-by-zone basis asthe vehicle moves across the lighting area.

Turning to FIG. 13, which shows the logic of the host computer. Afterinitialization 250, the host computer enters a cycle in which it firstchecks the ambient light intensity and sets the lighting devicesaccordingly (252, 254, 256, 258). Afterwards the intensity setting ofthe lighting devices may be manually overridden (260, 262) if desired bya controller of the system. After the intensity of the lighting deviceshas been set the host computer proceeds to check the status of eachlighting device in the network logging their status or flagging thelighting device as defective if the lighting device fails to respond(264, 266, 268, 270, 272). After each lighting device has been checkedthe host computer evaluates the network to see if sufficient light isbeing provided in the lighting area. If the luminosity if below standardof below a critical level an appropriate message will be displayed tothe controller of the system.

1. A lighting device comprising a plurality of groups of light emittingdiodes, each of said groups of light emitting diodes containing one ormore light emitting diodes, each of said light emitting diodes beingconfigured so as to pass between an energized light emitting state and anon-energized state; luminosity measuring means for providing a standardluminosity reading at predetermined time intervals; controller means fortransferring, at predetermined time intervals, in response to saidstandard luminosity reading, one or more of said groups of lightemitting diodes between a first energized group wherein said lightemitting diodes are in said energized light emitting state and a secondnon-energized group wherein said light emitting diodes are in saidnon-energized state.
 2. A lighting device as claimed in claim 1, whereinsaid controller means is configured to maintain all of the lightemitting diodes in said first energized group when a predeterminedluminosity reading is provided by said luminosity measuring means.
 3. Alighting device comprising a plurality of groups of light emittingdiodes, each of said groups of light emitting diodes containing one ormore light emitting diodes, each of said light emitting diodes beingconfigured so as to pass between an energized light emitting state and anon-energized state; usage time measuring means for providing a usagetime measurement for each of said groups of light emitting diodes atpredetermined intervals; controller means for transferring, atpredetermined time intervals, in response to said usage timemeasurements, one or more of said groups of light emitting diodesbetween a first energized group wherein said light emitting diodes arein said energized light emitting state and a second non-energized groupwherein said light emitting diodes are in said non-energized state.
 4. Alighting device as claimed in claim 1, wherein said controller meansfurther comprises: means for detecting whether any of said groups oflight emitting diodes have become unable to pass between said energizedlight emitting state and said non-energized state, and transferring saidgroups to a third non-functional group.
 5. A lighting device as claimedin claim 3, wherein said controller means further comprises: means fordetecting whether any of said groups of light emitting diodes havebecome unable to pass between said energized light emitting state andsaid non-energized state, and transferring said groups to a thirdnon-functional group.
 6. A lighting arrangement comprising: two or morecircuit board means, each circuit board means having a projection axisand a plurality of light emitting diodes, such that any light emitted bythe light emitting diodes on each of said circuit board means isprojected substantially parallel to said projection axis; said circuitboard means being disposed such that each of said projection axes aredisposed at an angle to each other.
 7. A lighting arrangement as claimedin claim 6, wherein said angle is from 5 to 15 degrees.
 8. A networkcomprising: a host computer; and a plurality of light emitting diodelighting devices; said host computer comprising: means for transmittinga request for a status report from each of said light emitting diodelighting devices. and means for transmitting a signal to each of saidlight emitting diode lighting devices such that the host computer candirect how much light each of said lighting devices emits; and each ofsaid plurality of light emitting diode lighting devices comprising:means for receiving a request for a status report from said hostcomputer, creating said status report, and transmitting said statusreport to said host computer; and means for receiving a signal from saidhost computer and altering how much light said light emitting diodedevice emits in response to said signal.
 9. A network as claimed inclaim 8, wherein said status report comprises current luminositysetting, current actual luminosity output, current light emitting diodedegradation, current dirt accumulation, current number of light emittingdiode groups in use, current number of open-circuited light emittingdiode groups and current average usage time of light emitting diodegroups;
 10. A network comprising: a host computer; and a plurality oflight emitting diode lighting devices; said host computer comprising:means for transmitting a signal to each of said light emitting diodelighting devices such that the host computer can direct how much lighteach of said lighting devices emits; and each of said plurality of lightemitting diode lighting devices comprising: means for receiving a signalfrom said host computer and altering how much light said light emittingdiode device emits in response to said signal.
 11. A dirt detectionsystem for a transparent surface, comprising: an electromagneticradiation emitting means for emitting light; electromagnetic radiationmeasurement means for measuring light; said electromagnetic radiationemitting means and said electromagnetic radiation measurement meansbeing configured such that said electromagnetic radiation emitting meansemits a certain amount of electromagnetic radiation through saidtransparent surface, and said electromagnetic radiation measurementmeans measuring how much of said certain amount of electromagneticradiation is reflected by said transparent surface and comparing saidamount to a base measurement taken when said transparent surface is freeof dirt.
 12. A method for manipulating the light intensity in a tunnel,said tunnel comprising a lighting system comprising a plurality oflighting devices, said method comprising means for raising and lowering,in unison, the luminosity level of each of said devices.
 13. A lightingdevice as claimed in claim 1, wherein said controller means isconfigured to transfer one or more of said groups of light emittingdiodes to said first energized group to increase a luminosity output ofsaid lighting device, and to transfer one or more of said groups oflight emitting diodes to said second non-energized groups to decreasesaid luminosity output of said lighting device.
 14. A lighting device asclaimed in claim 3, wherein said usage time measurement is a cumulativeusage time measurement for each of said groups of light emitting diodes.15. A lighting device comprising a plurality of groups of light emittingdiodes, each of said groups of light emitting diodes containing one ormore light emitting diodes, each of said light emitting diodes beingconfigured so as to pass between an energized light emitting state and anon-energized state; controller means for transferring, at predeterminedtime intervals, in response to a standard luminosity reading, one ormore of said groups of light emitting diodes between a first energizedgroup wherein said light emitting diodes are in said energized lightemitting state and a second non-energized group wherein said lightemitting diodes are in said non-energized state.
 16. A lighting deviceas claimed in claim 15, wherein said controller means is configured tomaintain all of the light emitting diodes in said first energized groupwhen a predetermined luminosity reading is provided by said luminositymeasuring means.
 17. A lighting device comprising a plurality of groupsof light emitting diodes, each of said groups of light emitting diodescontaining one or more light emitting diodes, each of said lightemitting diodes being configured so as to pass between an energizedlight emitting state and a non-energized state; controller means fortransferring, at predetermined time intervals, in response to said usagetime measurements, one or more of said groups of light emitting diodesbetween a first energized group wherein said light emitting diodes arein said energized light emitting state and a second non-energized groupwherein said light emitting diodes are in said non-energized state. 18.A lighting device as claimed in claim 15, wherein said controller meansfurther comprises: means for detecting whether any of said groups oflight emitting diodes have become unable to pass between said energizedlight emitting state and said non-energized state, and transferring saidgroups to a third non-functional group.
 19. A lighting device as claimedin claim 17, wherein said controller means further comprises: means fordetecting whether any of said groups of light emitting diodes havebecome unable to pass between said energized light emitting state andsaid non-energized state, and transferring said groups to a thirdnon-functional group.
 20. A lighting device as claimed in claim 15,wherein said controller means is configured to transfer one or more ofsaid groups of light emitting diodes to said first energized group toincrease a luminosity output of said lighting device, and to transferone or more of said groups of light emitting diodes to said secondnon-energized groups to decrease said luminosity output of said lightingdevice.
 21. A lighting device as claimed in claim 17, wherein said usagetime measurement is a cumulative usage time measurement for each of saidgroups of light emitting diodes.